Rapidly-soluble sodium dichloroisocyanurate dihydrate tablet

ABSTRACT

Process for producing a rapidly-soluble, structurally-strong, storage-stable chlorine releasing tablet by compressing sodium dichloroisocyanurate dihydrate in a structure-forming apparatus with pressures from about 2,000 to about 10,000 p.s.i.

This is a division of application Ser. No. 385,907, filed Aug. 6, l973,now U.S. Pat. No. 3,956,444.

This invention relates to a process of producing a rapidly-soluble,structurally-strong, storage-stable tablet that resists deteriorationand dimensional change due to moisture, and supplies active chlorinewhen placed in an aqueous solvent, by compressing sodiumdichloroisocyanurate dihydrate in a mold, die, or press at a pressure ofabout 2,000 to about 10,000 p.s.i.

Chlorine-releasing agents that give off available chlorine when placedin water have been used as bactericides to kill bacteria and to preventtheir growth in swimming pools, portable water supplies and the like.Chlorination has been accomplished by a variety of means using gaseouschlorine, solutions of chlorine-releasing agents, or solid forms ofagents which release chlorine. The safest and most popularchlorine-releasing agents used are the solid compositions, which may bein either granular or tabletted form. Tablets are preferred overgranular materials because they obviate the need for measuring cups andeliminate the problem of spillage and storage of bulky materials.

The tabletted chlorine-releasing compositions so far produced, have beeneither rapid-dissolving or slow-dissolving. Rapid-dissolving tablets areeffective in supplying available chlorine quickly to pool water, forexample, in response to changing chlorine demands put upon the poolwater. Slow-dissolving tablets, on the other hand, are effective inmaintaining available chlorine in pool water at a given rate over longperiods of time.

Tabletted anhydrous sodium dichloroisocyanurate is an example of achlorine-releasing composition that is rapid-dissolving. Anhydroussodium dichloroisocyanurate tablets which have physical propertiessuitable for packaging and shipping are formed only with difficultyunder high pressures (around 60,000 p.s.i.). Use of these high pressuresresults in some decomposition of the anhydrous material causing adecrease of available chlorine in the final product. Once formed, thetablets are not dimensionally stable; that is, they swell and developstructurally weak efflorescent structures upon prolonged exposure tohigh humidities or small amounts of moisture. Furthermore, compositionscontaining anhydrous sodium dichloroisocyanurate have been successfullytabletted only when a lubricant such as boric acid (see U.S. Pat. No.3,120,378) or stabilizers such as boron oxide and sodium carbonate (seeFrench Patent 1,537,311) have been employed during the molding process.Such additives are objectionable in-so-far as they act as diluents andthereby decrease the available chlorine content of the compositions. Theadditives also act as impurities which are often undesirable. Theseprocesses do not overcome the basic drawback of tabletting anhydroussodium dichloroisocyanurate, namely, that it does not tablet easily atconventional pressures of about 15,000 to 25,000 p.s.i. Consequently,the above processes are not commercially feasible, since the pressuresneeded to tablet the anhydrous material to produce a satisfactory tabletput excessive strain on the tabletting machinery causing extensive wearof the tabletting machinery, and result in decomposition of thechlorine-releasing agent.

Takuo Shinshige (Japanese Patent Publication 196723198) discovered thatthe addition of water within a specific range enabled various types ofchlorocyanurate powders to be molded without the above problems, andallowed the subsequent granulation of the tablets to form granularmaterials with increased specific gravities. In one example, Shinshigewas able to continuously tablet sodium dichlorocyanurate when thecompound contained 4% to 14% moisture under a conventional compressionpressure of 1,000 kilograms/square centimeter (approximately 15,000pounds/square inch). This compression pressure, however, produces atablet with a relatively long dissolution time of around 15 minutes.Such dissolution times are not sufficient to immediately combatbacterial growth such as is encountered in the entire area of a swimmingpool. Dissolving times of 5 minutes or less are required for suchimmediate bacterial action. Consequently, the patentee granulates thismaterial and forms a faster dissolving, higher specific gravitymaterial. Granular material, however, when used as a chlorine-releasingagent lacks the simplicity and convenience afforded by a tablettedproduct.

Tabletted trichloroisocyanuric acid and tabletted calcium hypochloriteare examples of slow-dissolving chlorine-releasing tablets. Thesetablets have dissolution times ranging from hours to days, which permitsthe release of available chlorine at one specific rate over long periodsof time. This slow solubility rate, however, has insufficientflexibility to permit the tablets to be effective as a bactericide inresponding to rapid changes in chlorine demands put on pool wateroccassioned by variations in climate or swimmer load.

It is the object of the present invention to produce a rapidly-soluble,structurally-strong, storage-stable tablet which is easily formed andwhich is resistant to deterioration or dimensional change due tomoisture.

I have made the surprising discovery that a rapidly-soluble,structurally-strong, storage-stable tablet that resists structuralchanges due to moisture can be formed without loss of available chlorineby compressing sodium dichloroisocyanurate dihydrate in astructure-forming apparatus, such as a press, mold or die, at a pressureof about 2,000 to about 10,000 p.s.i. The sodium dichloroisocyanuratedihydrate tablets form easily without lubricants or stabilizers, andmaintains its dimensional stability for extended periods of time. Thetablets are easily dispersed and provide for the rapid release ofchlorine to meet varying sanitizing needs; these advantages previouslyhave not been available with other chlorine sources.

The term "sodium dichloroisocyanurate dihydrate" means a hydrated sodiumdichloroisocyanurate containing 14.1% by weight water of hydration.Hydrated sodium dichloroisocyanurate containing less than 14.1% byweight water of hydration may be mixed with the dihydrate in minorconcentrations and used in the process of the invention.

Tablets of sodium dichloroisocyanurate dihydrate are prepared by placingeither granular or crystalline sodium dichloroisocyanurate dihydrateinto a structure-forming apparatus such as a press, mold, or die andpressing them to form the chlorine-releasing tablets. The pressure usedto press these tablets will vary depending upon the rate at which thetablet is to dissolve. This rate is termed the "solubility rate" and isthe time it takes a tablet (1 diameter by 3/8 thick) to dissolve andescape from a 1/2 stainless steel mesh cage immersed in 1 liter ofswirling distilled water at 20° C. Rapidly-soluble tablets havesolubility rates of below 5 minutes and preferably between 0.5 and 3minutes. In general, the pressures necessary to obtain this rapidsolubility rate range from about 2,000 to about 10,000 p.s.i. Pressuresbetween 2,000 and 5,000 p.s.i. produce tablets with a solubility rate ofaround 30 seconds. Pressures above 5,000 but below 10,000 p.s.i. producetablets with solubility rates of a few minutes. Pressures below about2,000 p.s.i. do not produce an acceptable tablet. These tablets aregenerally difficult to remove from the die, they have weak corners andhave poor structural strength and hardness. Pressures above about 10,000p.s.i. should be avoided since these pressures produce tablets with slowsolubility rates, that is above about 5 minutes. Such slow solubilityrates are not effective to immediately combat bacterial growth, forexample, in the entire area of a swimming pool.

The tablet may contain conventional additives such as coloring matter,various dyes, perfumes and the like. These tablets do not requirefillers as do detergent tablets, even though the tablets of thisinvention may contain fillers to increase the size of the tablet forease of handling and dispensing. The desired additives are simplyblended with the sodium dichloroisocyanurate dihydrate and the blendedformulation is tabletted.

In the tabletting procedure of this invention, it has been found thatthe pressed material does not adhere to the dies, and there is nocapping during the pressing of the material. The term "capping" refersto the internal horizontal separation of the tablet into two or morepieces because of the adherence of these pieces to each of the dies. Thetablets may be easily removed from the die. The overall appearance isexcellent, with the tablets having strong corners and excellenthardness. In general, the use of standard dies is eminently satisfactorywithout special provision for rotation of the dies during the pressingoperation.

The tablet of this invention, may be used as a source of availablechlorine in treating swimming pools or in other applications whichrequire chlorine treatment of water.

When the sanitizer tablet of this invention is used in swimming pools,it is preferred to place the tablet in the pool skimmer. The skimmer isnormally used as the water intake of a recirculating system for constantpurification and circulation of pool water. The resulting intake waterconstantly flows over the tablet, rapidly releasing available chlorineinto the intake water stream.

The number of tablets added to a pool is that number which will replacethe active chlorine dissipated during normal pool use. When climaticconditions or heavy swimmer load result in excessive chlorinedissipation, additional tablets are merely added. The immediate additionand dissolution of the tablets to yield available chlorine is necessaryto prevent the growth of bacteria which are present in the water. Excessconcentrations of available chlorine in the pool that may irritate theeyes and mucous membranes of the swimmers are not produced. The tabletsdo not leave any unsightly, white residue on pool surfaces, as is thecase with slower-dissolving chlorine-releasing agents. Since the tabletsleave no residue, they are truly maintenance free.

Where a recirculating system is not used or the tablets cannot beconveniently used in this manner, or when water other than in swimmingpools is to be treated, the tablets may be added directly to the water.

When sanitizing bodies of water other than in swimming pools, the numberof tablets added to the aqueous solution is that number which will killthe bacteria which are present. When treating an aqueous solution forthe first time it is generally necessary to employ an excess of tabletsto superchlorinate the solution. This results in rapid and completedestruction of bacteria and prevents bacterial growth. After thisinitial dosage, tablets may be added to the solution in an amount whichmerely replaces the active chlorine dissipated so as to maintain thesolution virtually bacteria free.

The term "tablet" as used herein refers not only to that product whichis obtained by compressing sodium dichloroisocyanurate dihydrate in amold press or die to form a unitary pressed shape of any geometricconfiguration, but also refers to any product which is compressed into adense shape, whether or not this dense shape is subsequently left intactor whether it is subdivided into individual discrete pieces of smallersize.

The following examples are given to illustrate the present invention butare not deemed to be limiting thereof.

EXAMPLE 1-A Process of the Invention

Tablets of sodium dichloroisocyanurate dihydrate were prepared byplacing 15 grams of granular sodium dichloroisocyanurate dihydrate intoa Carver Laboratory Hand Press having a stainless steel die cavity. Atabletting force was applied through a mating stainless steel plunger.The tabletting force or pressure applied is set forth in Table I.Tablets (1 inch diameter by 3/8 inch thick) were tested for hardness ina Strong, Cobb, Arner Hand Tester. One tablet was placed in the HandTester and the force necessary to crush the tablet was measured.Hardness was not tested above 25 kilograms/square centimeter since thisis the normal strength required for packaging and handling. Thesolubility rate was measured by supporting one tablet (1 inch diameterby 3/8 inch thick) in a 1/2 inch stainless steel mesh cage which wassuspended in 1 liter of swirling distilled water at 20° C. The timerequired for the tablets to completely dissolve and escape from the meshcage was measured. Results are set forth in Table I.

                  Table I                                                         ______________________________________                                        Pressure                Hardness  Solubility                                  (PSI)   Tablet Appearance                                                                             (Kg)      (min.)                                      ______________________________________                                         5,000  Easy removal from die                                                                         >25       0.5                                                 porous                                                                        strong                                                                10,000  Easy removal from die                                                                         >25       3                                                   porous                                                                        strong                                                                ______________________________________                                    

This example shows that the sodium dichloroisocyanurate dihydratetablets produced with pressures of 5,000 and 10,000 p.s.i. displayedgood physical properties. They had strong corners, good hardness, easyremoval from the die and were rapidly-soluble.

EXAMPLE 1-B Comparative Process

The process of Example 1 was repeated except that granular anhydroussodium dichloroisocyanurate and trichloroisocyanuric acid were used inplace of sodium dichloroisocyanurate dihydrate. The results are setforth in Tables II and III.

                  Table II                                                        ______________________________________                                        Anhydrous Sodium Dichloroisocyanurate                                         Pressure                Hardness  Solubility                                  (PSI)   Tablet Appearance                                                                             (Kg)      (min.)                                      ______________________________________                                         5,000  Squeaky and difficult                                                                         13.5      1.5                                                 removal from die                                                              porous                                                                        weak corners                                                          10,000  Squeaky and difficult                                                                         22        3                                                   removal from die                                                              less porous                                                                   weak corners                                                          ______________________________________                                    

                  Table III                                                       ______________________________________                                        Trichloroisocyanuric Acid                                                     Pressure                Hardness  Solubility                                  (PSI)   Tablet Appearance                                                                             (Kg)      (hours)                                     ______________________________________                                         5,000  Easy removal from die                                                                           24      16                                                  porous                                                                        weak corners                                                          10,000  Easy removal from die                                                                         >25       20                                                  slightly porous                                                               weak corners                                                          ______________________________________                                    

The data in Table II shows that tabletted anhydrous sodiumdichloroisocyanurate was rapidly soluble and difficult to remove fromthe die. The tablets showed poor hardness and weak corners.

The data in Table III shows that tabletted trichloroisocyanuric acid wasvery slowly soluble and easy to remove from the die. The tablets had areasonable hardness but the corners were weak.

EXAMPLE 2

This example compares the resistance of anhydrous sodiumdichloroisocyanurate and sodium dichloroisocyanurate dihydrate tabletsto deterioration and dimensional change upon wetting or prolongedexposure to high humidities.

A fine water mist was sprayed for two hours onto sodiumdichloroisocyanurate dihydrate and anhydrous sodium dichloroisocyanuratetablets produced according to Example 1-A and Example 1-B. The sodiumdichloroisocyanurate dihydrate tablets of this invention remainedsubstantially unchanged. The anhydrous sodium dichloroisocyanuratetablets increased significantly in volume and developed a weak,efflorescent structure.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications are intended to be included within the scope of thefollowing claims.

What is claimed is:
 1. A rapidly-soluble, structurally-strong,storage-stable compressed tablet consisting essentially ofrapidly-soluble chlorine-releasing sodium dichloroisocyanurate dihydratewherein said tablet has been compressed at pressures from about 2,000 toabout 10,000 p.s.i. in the absence of lubricants or stabilizers, andresists deterioration or dimensional change due to moisture.
 2. Thetablet of claim 1 having a solubility rate of below 5 minutes.
 3. Thetablet of claim 1 having a solubility rate between 0.5 and 3 minutes.